The forming of powdered or granulated substances into coated and uncoated tablets constitutes a simple, valuable method of administrating such substances. Compression brings about a compaction which in many cases facilitates the delivery, storage and use of medicaments. One difficulty in the preparation of tablets lies in the fact that few substances can be directly compressed into tablets (cf. Gstirner, "Grundstoffe und Verfahren der Arzneibereitung," 1960, pp. 3-4). This is because most substances either are too sticky to permit smooth ejection of the tablets, or the substances cannot be bound together adequately by the pressures applied. A characteristic frequently encountered in many substances is that they stick to the tablet die to the punches, causing the tablets to be partially or completely pulled apart when the upper punch is raised. To circumvent these undesirable characteristics, adjuvants such as anti-adhesives, binders and parting agents are added in more or less great percentages to the ingredients used in the production of common tablets.
In a number of applications, however, the addition of tableting adjuvants is undesirable or impossible. For example, in the case of effervescent tablets the conventional adjuvants produce a certain degree of turbidity on account of their poor solubility in water. In the case of troches, however, the taste of the tableting adjuvants is often unpleasant. Other disadvantages may lie in a change in the dissolving speed of the tablet, in an adverse effect on the stability of the ingredients, and in the enlargement of the total mass of the tablet. In the case of medicaments and dietetic nutrients, the addition of adjuvants must be declared on the label according to law, and the consumer who sets great store by purity will steer clear even of harmless additives. Consequently, a number of attempts have been made to modify the prior-art tableting processes so as to enable tablets to be made without the addition of adjuvants.
It is known that tablets have less tendency to stick to the tablet die and to the punches if the tablets are compressed under very high pressures. The disadvantages of this method is that the tablet substances begin to sinter, so that the porosity of the tablet is destroyed, and very hard, poorly soluble tablets result, which also have a tendency to "cap" or split.
In one special process the contact surfaces of the punches are coated with a plastic substance to diminish adhesion forces and thus prevent sticking. Due to the high pressures required especially for the pressing of troches, however, these plastic surfaces are deformed relatively rapidly and ground away by the abrasive action of the substances being tableted. The resulting inaccuracy of tablet size and the necessary frequent replacement of the punches and dies militate against widespread technical use of this method.
Attempts have furthermore been made to utilize the movement of the lower punch for the purpose of lubricating the die walls with a liquid lubricant such as paraffin or silicone oil. The lubrication of the punch surfaces, however, cannot simultaneously be accomplished in this manner, so that, in spite of the great technical expense that is necessary, there are great difficulties involved in tableting by this method.